For some limnological and oceanographic studies it is important that underwater samples be taken and that such samples be protected against dilution or modification due to leakage of the sampler during retrieval of the latter. One type of sampler designed for this purpose comprises a hollow tube, normally open at both ends, and having end closures or stoppers which are adapted to be moved from open positions to sealing positions in response to the dropping of a weighted messenger along the line or cable which supports the sampler. The stoppers are latched in their open positions via a latch which has a release mechanism that is tripped by compressive force generated by the weighted messenger to enable the stoppers to move to their closed positions. Such a latch mechanism is disclosed in U.S. Pat. No. 3,949,497, granted Apr. 13, 1976.
Although commercially successful, this latch mechanism has its limitations, particularly in those instances in which the support line is inclined to the vertical at such an angle as to prevent downward movement of the weighted messenger at a rate of speed to strike the release mechanism with a force sufficient to trigger the release mechanism.
Because of the necessity of maintaining the support line in a position in which the messenger may travel downward at the necessary speed to actuate the release mechanism, conventional samplers may not be used in those instances in which high currents cause the sampler support line to assume an adverse angle to the vertical.